Curriculum, to a great extent shapes students' experiences in school. Assessment as a major component of curriculum plays an important role in students' academic life because it not only assesses students learning but also contributes in their learning. Unfortunately, there are many issues in our curriculum, teaching learning and assessment. Almost in all the public and private schools, government prescribed textbooks are the only source of knowledge that are followed religiously, which provides one-sided, limited and outdated knowledge to the learners. Teachers are transmitting knowledge and there is no connection of teaching and learning with learners' daily lives. Moreover, assessment encourages rote learning and tests only knowledge, neglecting other higher order skills. The purpose of this research was to explore the success and challenges of three private schools in Karachi, Pakistan, who have initiated the Aga Khan University- Examination Board (AKU-EB) based portfolio assessment in their schools. The design of the research was a qualitative paradigm case study. One hundred and eleven students from all three schools, along with head teachers, and mathematics teachers of each school participated in this research. Besides students and teachers, one of the AKU-EB officials was the research participant. For data generating, I conducted semi-structured interviews of the teachers, head teachers and AKU-EB official and surveyed the students through a questionnaire. The findings revealed the portfolio assessment minimised teacher centered teaching approaches and promoted students active participation in teaching and learning. Use of reflection, self-assessment, peer assessment, presentation, and a collaborative learning environment in a school were major successes of this project. Stakeholders also a highlighted a few challenges regarding conducting and assessing group work, self – and peer - assessment. Stakeholders also faced challenges because of limited time available for the projects and ambiguity in the instructions for some projects.